Techniques for determining geolocations

ABSTRACT

The described geolocation techniques determine a location of an earth-based vehicle using a non-geostationary satellite. For instance, the non-geostationary satellite receives signals transmitted by the earth-based vehicle, determines the arrival times of the signals, and the position information of the satellite corresponding to the arrival times of the signals. The arrival times and position information of the satellite are sent to a signal processing unit to determine a location of the vehicle.

TECHNICAL FIELD

The following disclosure relates to systems, methods, and devices fordetermining geolocations.

BACKGROUND

A target vehicle's location can be determined by detecting and locatingsignals from an emitter onboard the target vehicle. In particular, aconventional technique known as the “direction finding (DF) technique”uses directional antennas to create lines of positions (LoPs) to signalsources. The DF technique requires these LoPs to be taken from multiplemeasurement vehicles that have known locations. The locations of thesemeasurement vehicles along with the created LoPs are then used todetermine a Position Fix (PF), a location determine in two-dimensionspace, of the emitter onboard the target vehicle. The conventional DFtechnique, however, introduces errors to the determined PF when thetarget vehicle's emitter moves between the LoP measurements. This errorcan be eliminated by configuring the multiple measurement vehicles totake LoPs simultaneously. But, using multiple measurement vehicles canincrease the cost of operation. For example, to obtain multiplemeasurements, a system employing the conventional DF technique mayrequire two or three vehicles that can measure a signal transmitted froma signal source on the target vehicle. Furthermore, multiple vehiclescan have a limited duration of operation, in part, because vehicles havea limited fuel range.

Another conventional technique for determining a target vehicle'slocation is known as “Blind Coherent Integration.” This techniqueinvolves multiple measurement vehicles that are configured to receivesignals, including ones emitted by the target vehicle. The signalsreceived at each of the sensing devices are added together aftercompensating for time delay and doppler frequency offset associated witheach signal. The summation process causes the signals from the sametarget vehicle to be coherently added, becoming strengthened, whileother signals are added incoherently, becoming canceled due torandomness of the time delays and doppler frequency offsets. Theresulting signal after the summation process can be used to determinethe location of the target vehicle.

SUMMARY

The disclosed techniques can use a single non-geostationary satellite,such as a CubeSat, to determine a geolocation of an earth-based vehicle(e.g., a boat, a ship, or a truck) in three-dimensions on the earth'ssurface by detecting a signal transmitted by an emitter on theearth-based vehicle. Based on the determined location, the satellite candirectionally or timely transmit a signal to control the earth-basedvehicle for an autonomous driving application.

A system for performing geolocation can include a non-geostationarysatellite and a signal processing unit. The non-geostationary satellitemay orbit earth in a non-geostationary path, such as in a low-earthorbit (LEO), a medium-earth orbit (MEO), a high-earth orbit (HEO), or aMolniya orbit. The non-geostationary satellite includes a datacollection apparatus with a processor that receives a number of signalsfrom an earth-based vehicle and determines their arrival times, andobtains the non-geostationary satellite's position informationcorresponding to the signals' arrival times. The data collectionapparatus also sends, to a signal processing unit, the arrival times andthe position information of the non-geostationary satellitecorresponding to the received signals.

Upon receiving the arrival times and positioning information, the signalprocessing unit is configured to determine a location of the earth-basedvehicle. The signal processing unit uses the received information toselect a plurality of candidate locations to determine the location ofthe earth-based vehicle. The signal processing unit also determines, foreach candidate location and based on the arrival times and the positioninformation, an error value representing the proximity between acandidate location and the location of the earth-based vehicle. Thesignal processing unit selects, from the plurality of candidatelocations associated with a plurality of error values, one candidatelocation having a lowest error value, which determines the location ofthe earth-based vehicle.

In other aspects, the above-described methods can be embodied in theform of processor-executable code and stored in a computer-readableprogram medium.

A device that is configured or operable to perform the above-describedmethods is also disclosed.

The above and other aspects and their implementations are described ingreater detail in the drawings, the descriptions, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example of a technique for determining a geolocationusing a single moving satellite.

FIG. 2 is a block diagram of an example of a data collection apparatusthat receives and processes received signals.

FIG. 3 shows a block diagram of an example of a signal processing unitthat can determine a location of an earth-based vehicle.

FIG. 4 shows an example flow diagram for receiving and processingreceived signals.

FIG. 5 shows an example flow diagram for determining a location of anearth-based vehicle.

DETAILED DESCRIPTION

The techniques for determining a geolocation described herein can beused to gather positional information about a moving or stationaryvehicle through passive detection of signals transmitted by a signalsource on the vehicle. A geolocation system can be installed andoperated on a space-based vehicle, such as a non-geostationary satelliteto detect signals transmitted from an earth-based vehicle operating asignal source. The non-geostationary satellite may orbit earth in anon-geostationary path, such as in a LEO, a MEO, a HEO, or a Molniyaorbit. Based on the signals detected by the satellite, a signalprocessing unit can use the disclosed techniques to determine thegeolocation of an earth-based vehicle. The signal processing unit can belocated on the satellite, or on a remote platform which may be moving(e.g., aircraft), or stationary (e.g., on the earth). Thus, a singlesatellite can use the technologies described herein to performmeasurements that in turn are used by a signal processing unit todetermine the geolocation of an earth-based vehicle. Unlike conventionaltechniques that uses multiple measuring vehicles (e.g., multipleaircrafts) to determine a location of a signal source in two-dimensions,the disclosed technology can use a single satellite to determine of alocation of an earth-based vehicle in three-dimensions.

LEO satellites can operate at an altitude from about 100 miles toapproximately 1,240 miles above the earth's surface. LEO has an orbitwith period of approximately less than 128 minutes. LEO may be anelliptical orbit or a circular orbit. For a circular orbit, an LEO mayhave a maximum altitude of approximately 1269 miles and a minimumaltitude of approximately 124 miles. Since a LEO satellite moves atrelatively fast speeds over the ground (e.g., approximately 14,430 mphto 17,450 mph for a circular orbit), multiple measurements can be takenby the same LEO satellite from different locations faster than what ispossible using an aircraft-mounted conventional measurement system. Thespeed of the LEO (and similarly MEO, HEO, or Molniya orbit) satellitecan be considered relatively fast when compared to a speed of a movingor stationary earth-based vehicle.

As an example, a geolocation system on an non-geostationary satellitecan include a wide-spectrum or bandwidth capability because operatingfrequencies of signal sources are initially unknown, a wide dynamicrange because signal strength is initially unknown, a narrow bandpass todiscriminate the signal of interest from other signal sources on nearbyfrequencies, and/or a capability to measure an angle-of arrival toobtain bearings to locate the transmitter. The bandwidth of thegeolocation system on the non-geostationary satellite can be designed toreceive signals transmitted within a frequency spectrum that ranges fromapproximately 30 MHz to approximately 50 GHz.

FIG. 1 shows an example of a geolocation technique using a single movingsatellite. Satellite 102 is a single non-geostationary satellite thatoperates and moves in a non-geostationary orbit. A non-geostationarysatellite can travel in an orbit around the earth at a speed faster thanthe earth's rotation. FIG. 1 shows the satellite 102 traversing ormoving along a known dotted satellite path from position A to B to C toD.

In this example, the satellite 102 includes one or more antennas and areceiver that can be configured to receive signals emitted in afrequency range of 30 MHz to 50 GHz. Specifically, in some embodiments,the antenna and receiver of the satellite 102 can be configured toreceive signals emitted in a frequency range of 2 GHz to 18 GHz. Severalsignal sources operate at frequencies between 2 GHz and 18 GHz. Someexamples of a satellite 102 operating in a non-geostationary orbitinclude a CubeSat or a NanoSat. A CubeSat is a small form factorsatellite that may include several systems to operate the CubeSat forvariety of purposes. For instance, a CubeSat may include a power source,such as a battery and/or solar panels, a communication system (e.g., anantenna), and additional electronics (e.g., signal processors orsensors). A NanoSat may be smaller in size compared to a CubeSat and mayinclude many of the systems included in the CubeSat.

Target location T represents a location of an earth-based vehicle 104,such as a ship, or a truck. The four lines drawn between the satellite102, when it is at positions A, B, C, and D, and the earth-based vehicle104, represent signals that are transmitted from a signal sourceoperating on the earth-based vehicle 104 and that are received by thesatellite 102. For example, the four lines can represent signals from aship's signal source system signature. Additional signals that may bereceived in-between locations A, B, C, and D are omitted from FIG. 1 forthe sake of clarity. The geolocation techniques described in this patentdocument can determine the target location T in three-dimensions.

The non-geostationary satellite 102 can be considered relatively fast(when compared to a speed of a relatively slowly moving or stationaryearth-based vehicle 104), which is a beneficial feature for determininggeolocation. A conventional aircraft-based system can be susceptible tolarge errors in determining location of a vehicle in scenarios where theaircraft-based system measures the received signals from the vehiclethat moves during the time period when the measurements are taken. Thesmall difference in speeds between the flying aircraft and the movingvehicle can introduce errors in location accuracy. In contrast, thelarge difference in speeds between a fast-moving non-geostationarysatellite 102 and a relatively slowly moving or stationary earth-basedvehicle 104 is beneficial, at least because the non-geostationarysatellite 102 can receive multiple signals from the earth-based vehicle104 whose relatively slow speed minimizes the errors in determining thevehicle 104's location. As further explained below, the informationassociated with multiple signals can be processed by a signal processingunit to locate a position or location of the earth-based vehicle 104,which is different from the conventional technique of correlatingbearings.

In FIG. 1, the earth-based vehicle 104 may be located at an unknowntarget location T on the earth's surface. The bottom half of FIG. 1shows two related timing diagrams. The top timing diagram illustratesthe Target (or earth-based vehicle 104) transmitting signals severaltimes including at times t₀, t₁, t₂, t₃, etc., The difference betweenthe signals transmitted by the vehicle 104 is shown as t_(R). The timedifference between t₀ and t₁ can be described as t₁=n*t_(R), the timedifference between to and t₂ can be described as t₂=m*t_(R), and thetime difference between to and t₃ can be described as t₃=o*t_(R). Thevariables n, m, and o may be integer values.

In timing diagram example of FIG. 1, t_(R) is constrained by the signalsource on the vehicle 104 and can be a constant or may have an unknownvalue. In some cases where t_(R) is irregular but deterministic, thelocation determination techniques described in FIG. 3 below can be usedto determine location of the earth-based vehicle 104. For the case of asignal source, the repetition period t_(R), is a signature of the signalsource used by the vehicle 104. The transmit signals could be single ormultiple depending on the signal sweep rate (rotation rate) or pulserepetition rate (PRR) of the multiple signals. The sweep rate, PRR andindividual radio frequency (RF) signal pulse width are functions of aparticular signal source set. Other signals with known or deterministicproperties can also be received and processed to determine location ofthe earth-based vehicle.

The bottom timing diagram in FIG. 1 illustrates the satellite 102receiving at least some of the signals transmitted by the earth-basedvehicle 104 at satellite locations A, B, C, and D. For instance, thesignals transmitted by the vehicle 104 at to is received by thesatellite 102 at time of arrival t_(A) and at satellite location A, thesignal transmitted by the vehicle 104 at t₁ is received by the satellite102 at time of arrival t_(B) and at satellite location B, and so on. Thetime differences t_(A)-t₀, t_(B)-t₁, and so on are the difference intime between when the transmitter transmits a signal and the receiverreceives that same signal. The signals received at times t_(A), t_(B),t_(C), t_(D) need not be from consecutive transmitted signals.

The satellite 102 may include a Global Positioning System (GPS) devicethat provides information about positions A, B, C, and D of thesatellite 102 when the satellite 102 received the signals from theearth-based vehicle 104. As further described in FIG. 3 below, a signalprocessing unit processes the signals received by the satellite 102 todetermine a target location T in three dimensions.

FIG. 2 is a block diagram illustrating an example of a data collectionapparatus located on or in an non-geostationary satellite that may orbitin a non-geostationary orbit, such as in a LEO, MEO, HEO, or Molniyaorbit. The data collection apparatus 200 includes one or more processors220 that can read code from the memory 210, and perform operationsassociated with the other blocks or modules shown in FIG. 2. The datacollection apparatus 200 includes one or more antennas 230 and areceiver 240 configured to receive the transmitted signals. For example,the receiver 240 can receive the signals at times t_(A), t_(B), t_(C),t_(D), etc., as mentioned in FIG. 1 while the non-geostationarysatellite moves in between each received signal.

Based on the received signals, the data collection module 250 collectsdata associated with the received signals. For example, referring to thesignal received by the data collection apparatus 200 at position A inFIG. 1, the data collection module 250 obtains the time t_(A) when thesignal was received. The data collection module 250 also obtainsinformation regarding the location of the non-geostationary satellite102 at position A from a satellite location module 260 (e.g., GPS chipor a position location determination device, such as inertial guidanceor derived from other externally provided positional informationavailable to it). The satellite location module 260 can calculatesatellite location from data or information available externally to thesatellite. The satellite may, for example, have ephemeris datainformation uploaded to it from which the satellite location module 260could calculate the satellite's position at the time of arrival of asignal. The satellite location module 260 can have information based onsignal source location information (e.g., ground signal-sourceinformation) uploaded to it from which to calculate the satellite'sposition. The data collection module 205 also collects timing andsatellite position data associated with each signal received at timest_(B), t_(C), and t_(D), and any additional signals.

The data collection apparatus 200 also includes a transceiver 270 (orother receivers and transmitters) with which the satellite 102 cancommunicate with a stationary platform (e.g., ground-based computingdevice located on earth) or with a moving remote platform (e.g., anaircraft). The computing device can communicate to the satellite 102 viathe transceiver 270 to instruct the data collection module 250 tocollect data associated with the received signals (e.g., arrival timesand/or position information of the satellite) or to send that data tothe computing device. In some embodiments, the transceiver 270 can becombined with the receiver 240 (e.g., may be the same device) so thatthe transceiver 270 can perform the operations associated with thereceiver 240. The data collection module 250 is configured to collectand/or send data associated with the received signals in response toreceiving an instruction from the computing system located on astationary platform (e.g., ground-based on the earth) or located on aremote moving platform (e.g., an aircraft). The computing device cansend the data received from the data collection module 250 to a signalprocessing unit (as shown in FIG. 3) that can determine the location ofthe earth-based vehicle 104. The signal processing unit can be locatedin a stationary platform (e.g., the ground-based computing system onearth) or the signal processing unit can be located on or in a movingremote platform-based computing device. In some other embodiments, thesatellite 102 can include a signal processing unit (as shown in FIG. 3)that can determine a location of the earth-based vehicle 104. Inembodiments where the signal processing unit is included in thesatellite 102, the determined location of the earth-based vehicle 104 issent to the computing device in a stationary platform (e.g., aground-based computing device located on earth) or in a moving remoteplatform.

FIG. 3 shows an example of a signal processing unit that can determine alocation of an earth-based vehicle. The signal processing unit 300 mayinclude one or more processors 320 that can read code from the memory310, and perform operations associated with the other blocks or modulesof the signal processing unit 300. In embodiments where the datacollection apparatus 200 and signal processing unit 300 are located onor in an non-geostationary satellite, the memory 210 and 310 may be thesame and the processor(s) 330 and 330 may be the same.

The signal processing unit 300 includes a location determination module340 that obtains signal timing (e.g., arrival time) and satelliteposition data from the data collection module 250. In embodiments wherethe signal processing unit 300 is located on a stationary platform(e.g., ground-based on the earth) or on a moving remote platform (e.g.,an aircraft), the receiver 330 receives the signal timing and satelliteposition data from the data collection module 250. Based on the receivedtiming and position data, the location determination module 340determines the location of the earth-based vehicle 104 using thetechniques described below.

The location determination module 340 can determine the location of theearth-based vehicle 104 based on the operations described below. Adetailed explanation of the computations, relevant equations, andadditional operations to determine location of the earth-based vehicleis described after the operations described below (and elsewhere in thispatent document).

-   -   The location determination module 340 chooses a candidate        location and determines a first set of path lengths between the        candidate location and each satellite position data associated        with a received signal (as explained in FIG. 1). For instance,        the first set of path lengths may be obtained by determining a        magnitude of the vector between the candidate location and each        of the satellite position data.    -   The location determination module 340 also determines a second        set of path lengths between a location of the earth-based        vehicle 104 and each satellite position data. For instance, the        second set of path lengths may be obtained by multiplying the        speed of light with the arrival time of each signal.    -   Next, the location determination module 340 obtains two error        values. The first error value (described as path length error        value below) is obtained by comparing path lengths from the        first set with the corresponding path lengths from the second        set. The second error value (described as earth-radius error        value below) is obtained by taking the difference between the        radius of the earth known at the latitude and longitude        associated with the candidate location and the magnitude of the        radius of the candidate location determined from the same        reference point, e.g., the center of the earth. The two error        values are combined to obtain a total error that characterizes        the proximity between the candidate location and the actual        location of the earth-based vehicle 104.    -   The operations described above can be repeated by using        additional candidate location values to obtain total error        values corresponding to the additional candidate locations. The        candidate location associated with the lowest total error is        select as the best determine of the location of the earth-based        vehicle 104.

Referring to FIG. 1, the values for variables t₀, t_(R) and Targetlocation T are unknown. In the timing diagram example shown in FIG. 1,the satellite 102 can obtain four measurements, for example, foursatellite position and four arrival times related to the signalsreceived at times t_(A), t_(B), t_(C), t_(D). Based on the satelliteposition and timing data, the location determination module 340 usesEquation (1) to determine target location T.

(|TD|−|TB|)−(|TC|−|TA|)=c×[t _(D) −t _(B)−(t _(C) −t _(A))]  Equation(1)

where “c” is the speed of light, |TA| is the magnitude of the vector TA,which is the path length or distance from T to A, |TB| is the magnitudeof the vector TB, which is the path length from T to B, and so on. Thevariables n, m and o (as shown in FIG. 1) are integers that relate tothe transmit times t₁, t₂, and t₃, respectively, from Target T. Asmentioned above, the scenario in FIG. 1 shows that there are threeunknown quantities: t₀, t_(R), and target location T.

The location determination module 340 can eliminate to and t_(R) by anexample algebraic manipulation as shown in Equation (1) below, leavingthe target location T as the only unknown. Thus, in some embodiments, asexplained for Equation (1), a signal processing unit 300 uses at leastfour received signals to solve for the target location T.

In some other embodiments, to and t_(R) can be eliminated using onlythree measurements, t_(A), t_(B) and t_(C). Thus, Equation (1) becomesEquation (2) below.

(|TC|−|TB|)−(|TB|−|TA|)=c×[t _(C)−2·t _(B) +t _(A)]  Equation (2)

Thus, in some embodiments, as explained for Equation (2), a signalprocessing unit 300 uses at least three received signals to solve forthe target location T.

A benefit of using Equation (1) to determine target location T is thatEquation (1) can eliminate to and the repetition period, t_(R) withoutknowing the values of to and t_(R). Similarly, Equation (2) can be usedto determine target location T so that Equation (2) can eliminate to andthe repetition period, t_(R) without knowing the values of to and t_(R).

To determine a target location T in three dimensions, the locationdetermination module 340 can select a candidate target location, T′. Thecandidate target location T′ can be associated with a latitude, alongitude, a height at or above the surface of the earth. The latitudeand longitude of T′ may be based on a reference system known as WorldGeodetic System 1984 (WGS 1984). An example of an initial target heightis sea level. Candidate target location T′ can be selected based on anumber of factors such as the range of elevation (e.g., 0 to 30 degrees)from the earth-based vehicle to the satellite that receives the signals,or the doppler frequency of the received signals.

Next, the location determination module 340 constructs a path lengtherror function as shown in Equation (3) below for embodiments using atleast four received signals. In some embodiments, the locationdetermination module 340 constructs a path length error function asshown in Equation (4) below using at least three received signals.

|T′D|−|T′B|−(|T′C|−|T′A|)−c×[t _(D) −t _(B)−(t _(C) −t_(A))]=ε_(p)  Equation (3)

|T′C|−|T′B|−(|T′B|−|T′A|)−c×[t _(C)−2t _(B) +t _(A))]=ε_(p)  Equation(4)

where ε_(p) is a value that describes or represents the path lengtherror, |T′A| is the magnitude of the vector T′A, which is the pathlength or distance from T′ to A, |T′B| is the magnitude of the vectorT′B, which is the path length from T′ to B, and so on. As an example,|T′D| can be determined by converting the latitude and longitude of T′to geocentric cartesian coordinates (e.g., (x, y, z) which may betranslated into <radius, latitude, longitude>), where T′ is the vector(x, y, z). Similarly, the latitude and longitude of D obtained from GPScoordinates for example are converted to geocentric cartesiancoordinates to obtain vector D. T′D is the vector between T′ and D, and|T′D| is the magnitude or length of the vector that describes orrepresents the distance between T′ and D.

As shown in Equations (3) and (4), the path length error value ε_(p), isthe difference between (i) the path lengths from a candidate location,T′ to the locations of satellite (e.g., as calculated from thesatellite's locations relative to candidate location T′ at theobservation time (e.g., |T′D|−|T′B|−(|T′C|−|T′A|) for Equation (3)) and(ii) the path length calculated from the time of arrival of the signalsreceived from target location T (e.g., c×[t_(D)−t_(B)−(t_(C)−t_(A))] forEquation (3)). The path lengths |T′A|, |T′B|, |T′C|, and/or |T′D| can beconsidered a set of path lengths between the candidate location T′ andeach position of the non-geostationary satellite. Furthermore, the pathlengths (c×t_(A)), (c×t_(B)) or (c×2t_(B)), (c×t_(C)), and/or (c×t_(D))can be considered another set of path lengths between the location ofthe earth-based vehicle and each position of the non-geostationarysatellite.

Equation (3) is the same as Equation (5) shown below. Equations (3) and(5) can be solved by first determining for each satellite location (e.g.positions A, B, C, D) a difference between a path length associated witha candidate location T′ and a path length associated with signalsreceived from target location T (e.g., (|T′D|−c×t_(D)), (|T′B|−c×t_(B)),(|T′C|−c×t_(C)), (|T′A|−c×t_(A))). Next, path length error value ε_(p),is determined by subtracting the differences between the path lengthsassociated with positions B, C, and D and by adding the differencebetween the path length associated with position A.

(|T′D|−c×t _(D))−(|T′B|−c×t _(B))−(|T′C|−c×t _(C))+(|T′A|−c×t_(A))=ε_(p)  Equation (5)

Similarly, Equation (4) is the same as Equation (6) shown below.

(|T′C|−c×t _(C))−(2|T′B|−c×2t _(B))+(|T′A|−c×t _(A))=ε_(p)  Equation (6)

The location determination module 340 can minimize the path error valuefor Equations (5) or (6) by iterating candidate values of T′ usingEquation (8) as described below. By minimizing the path length errorvalue, the location determination module 340 can determine the targetlocation T in three dimensions.

Next, the location determination module 340 can use another errorfunction to determine the target location T in a third dimension, suchas height. Since the Target position, T, is constrained to be on or nearto the earth surface, the location determination module 340 canconstruct an example earth-radius error function as shown below inEquation (7), where ε_(r) is a value that describes or represents theearth-radius error, |T′| is the length of the vector T′ can bedetermined from a reference point (0, 0, 0) in geocentric coordinates(i.e., center mass of earth). |T′| describes the magnitude of the radiusof the candidate location T′, which can be determined by taking thesquare root of the sum of the squares of the cartesian coordinates ofT′, i.e., square root(x²+y²+z²). The earth-radius error value ε_(r) canbe the radial difference between the length of the vector T′ and theearth's radius, r_(e). The earth's radius r_(e) is determined at thelatitude and longitude location associated with candidate location T′(as given by, e.g., WGS-84) and can be determined from a reference point(0, 0, 0).

|T′|−r _(e)=ε_(r)  Equation (7)

Next, the location determination module 340 can combine the two sets oferror quantities obtained from the path error and earth radius errorfunction values in a mean squared error (MSE) form as shown in Equation(8).

mse=ε _(p) ²+(k×ε _(r) ²)  Equation (8)

where k is a scale factor or a weighting value. In some embodiments, kmay have a pre-determined value, such as 1. The MSE provides a valuethat can characterize the proximity or the closeness between thecandidate location T′ and the actual target location T. Thus, the MSEcan quantify whether the candidate location T′ is a good determine ofthe target location T. Thus, a low value for MSE indicates that thecandidate location T′ is close to the actual target location T.

The location determination module 340 can minimize the combined errorquantities to determine a best determine of the target location T inthree dimensions. The location determination module 340 can determinethe best determine of target location, T, by iterating candidate valuesof T′ and by using the set of measurements taken by the satellite for avehicle located at target location T. For example, the locationdetermination module 340 can repeat Equations (6) to (8) (or Equations(5), (7), and (8)) two times by using two different values of T′ (e.g.,a first T′ and a second T′) and by using the same set of measurementstaken by the satellite for a vehicle located at target location T toprovide a first MSE for the first T′ and a second MSE for the second T′.In this example, the location determination module 340 can select eitherthe first or the second T′ that has the lowest MSE. In some embodiments,the location determination module 340 may iterate the candidate valuesof T′ many times (e.g., four times) to provide a best determine of thetarget location T. In some example embodiments, the locationdetermination module 340 may iterate candidate values of T′ to determineof Target location, T by using a minimization technique such as a DownHill Simplex method.

The signal processing unit 300 may include a location tracking module350 that can store the candidate location T′ that best determines thetarget location T of the earth-based vehicle determined by the locationdetermination module 340. A benefit of storing the best determine of thetarget location T is that it can provide a history of the determinedlocation(s) of the earth-based vehicle. A ground-based or remoteplatform-based computing device may use the location history of theearth-based vehicle to plot a map that shows the various locations ofthe earth-based vehicle at different times.

In some embodiments, to enhance the accuracy of the determine of thetarget location T, the location determination module 340 can repeat theoperations described above in the context of Equations (1) to (8) usingadditional position and timing measurements that may be obtained by thesatellite in sequence. As explained above, a location determinationmodule 340 can use the four measurements described in FIG. 1 (related tosatellite locations A, B, C, and D) to determine a target location T. Insome cases, the satellite 102 may receive additional signals fromvehicle 104 at additional satellite locations E, F, G, H (not shown inFIG. 1). In such cases, the determine of the target location T can beimproved by using information associated with the additional signals.For example, the location determination module 340 can use the fourmeasurements related to satellite location B, C, D, and E to obtainanother determine of the target location T. In another example, thelocation determination module 340 can use the four measurements relatedto satellite location E, F, G, and H to obtain another determine of thetarget location T.

The techniques described in this patent document can be used todetermine a location of an earth-based vehicle (e.g., boat, ship, ortruck) based on timing and position measurement data associated withsignals received by a receiver on a non-geostationary satellite. Forexample, based on the signals transmitted by a signal source on avehicle, the location determination module 340 can determine a locationof the ship from which the signal source is operating. In someembodiments, the techniques described in this patent document can beextended to a multi-satellite system involving multiplenon-geostationary satellites. Since a satellite moves fast compared to aslowly moving earth-based vehicle, a single satellite travelling aroundthe earth cannot receive signals from a vehicle located on the earth atall times. In a multi-satellite system, each non-geostationary satellitecan be configured to obtain multiple measurement data as described inthis patent document. Each non-geostationary satellite can orbit theearth at some distance from another non-geostationary satellite so thatthe multiple satellites can form multiple rings of moving satellitesorbiting the earth. The location determination module 340 of the signalprocessing unit can obtain the multiple measurement data from eachsatellite to determine location of an earth-based vehicle operating asignal source. A benefit of the multi-satellite system is that it canallow a signal processing unit to continuously determine the location ofa moving or stationary earth-based vehicle operating a EM source.

FIG. 4 shows an example flow diagram for receiving and processingsignals by a data collection apparatus. At the receiving operation 402,a data collection apparatus on a non-geostationary satellite receives anumber of signals from an earth-based vehicle. The non-geostationarysatellite may orbit earth in a non-geostationary orbit, such as in aLEO, MEO, HEO, or Molniya orbit. In some embodiments, the number ofsignals is at least three.

For each received signal, the data collection apparatus determines anarrival time and a position information of the non-geostationarysatellite. At the determining operation 404, the data collectionapparatus determines arrival times of the number of signals. At theobtaining operation 406, the data collection apparatus obtains positioninformation of the non-geostationary satellite corresponding to thearrival times of the number of signals. The determining operation 404and the obtaining operation 406 may be performed after each signal hasbeen received. In some embodiments, the position information of thenon-geostationary satellite is obtained from a global positioning system(GPS) device located on the non-geostationary satellite.

At the sending operation 408, the data collection apparatus sends, to asignal processing unit, the arrival times and the position informationof the non-geostationary satellite for the number of signals. In someembodiments, the data collection apparatus may send each arrival timeand position information to a signal processing unit as the datacollection apparatus receives and processes each signal. In some otherembodiments, the data collection apparatus may send a group of arrivaltimes and position information (e.g., a set of 3 or 4 of arrival timesand a set of 3 or 4 position information) to a signal processing unitafter the data collection apparatus receives and processes a number ofsignals (e.g., 3 or 4). In some embodiments, the data processingapparatus is configured to perform the determining operation 404, theobtaining operation 406, or the sending operation 408 in response toreceiving an instruction from a ground-based or remote platform-basedcomputing system.

In some embodiments, the data collection apparatus may include aprocessor and a memory that may include instructions stored thereupon.The instructions upon execution by the processor configure the datacollection apparatus to perform the operations described in FIGS. 2 and4 and in the embodiments described in this patent document.

FIG. 5 shows an example flow diagram for determining a location of anearth-based vehicle by a signal processing unit. At the receivingoperation 502, the signal processing unit receives arrival times andposition information of a non-geostationary satellite associated with anumber of signals received by the non-geostationary satellite from theearth-based vehicle. In some embodiments, the signal processing unit islocated in a ground-based or in a remote platform-based computingsystem.

At the selecting operation 504, the signal processing unit selects aplurality of candidate locations (e.g., four candidate locations) todetermine the location of the earth-based vehicle.

At the processing operation 506, the signal processing unit processesthe arrival times, the position information, and the plurality ofcandidate locations to determine the location of the earth-basedvehicle. The processing of the arrival times, position information, andcandidate locations can be performed by determining, for each candidatelocation and based on the arrival times and the position information, anerror value that describes or represents a proximity between a candidatelocation and the location of the earth-based vehicle. In someembodiments, the error value is determined for each candidate locationby the signal processing unit configured to

-   -   (i) determine a first set of path lengths between the candidate        location and each position information of the non-geostationary        satellite,    -   (ii) determine a second set of path lengths between the location        of the earth-based vehicle and each position information of the        non-geostationary satellite,    -   (iii) obtain a first error value based on differences between        path lengths from the first set of path lengths and        corresponding path lengths from the second set of path lengths        for each position information of the non-geostationary        satellite,    -   (iv) obtain a second error value based on a difference between        earth's radius at a latitude and a longitude associated with the        candidate location and a magnitude of the candidate location's        radius, where the earth radius and the magnitude of the        candidate location's radius are determined from a same reference        point, and    -   (v) determine the error value by combining the first error value        and the second error value.

In some embodiments, the first set of path lengths are determined by thesignal processing unit configured to calculate a magnitude of a vectorbetween the candidate location and each position information of thenon-geostationary satellite. In some embodiments, the second set of pathlengths are determined by the signal processing unit configured tomultiply a speed of light by each arrival time of the number of signals,where the number of signals are received from the location of theearth-based vehicle.

In some embodiments, the first error value is obtained by the signalprocessing unit configured to use a linear combination of thedifferences between path lengths from the first set of path lengths andcorresponding path lengths from the second set of path lengths for eachposition information of the non-geostationary satellite. In someembodiments, the error value is determined by the signal processing unitconfigured to: multiply a pre-determined value by the second error valueraised to a power of two to obtain a first value, and add the firstvalue to the first error value raised to a power of two to obtain theerror value

After the processing operation, the signal processing unit selects, fromthe plurality of candidate locations associated with a plurality oferror values, one candidate location having a lowest error value, wherethe selected candidate location is the determine of the location of theearth-based vehicle. In some embodiments, the selected candidatelocation provides the determine of the location of the earth-basedvehicle in three-dimensions. In some embodiments, the signal processingunit is further configured to store the selected candidate location forthe earth-based vehicle.

In some embodiments, the signal processing unit may include a processorand a memory that may include instructions stored thereupon. Theinstructions upon execution by the processor configure the signalprocessing unit to perform the operations described in FIGS. 3 and 5 andin the embodiments described in this patent document.

The disclosed and other embodiments, modules and the functionaloperations described in this document can be implemented in digitalelectronic circuitry, or in computer software, firmware, or hardware,including the structures disclosed in this document and their structuralequivalents, or in combinations of one or more of them. The disclosedand other embodiments can be implemented as one or more computer programproducts, i.e., one or more modules of computer program instructionsencoded on a computer readable medium for execution by, or to controlthe operation of, data processing apparatus. The computer readablemedium can be a machine-readable storage device, a machine-readablestorage substrate, a memory device, a composition of matter effecting amachine-readable propagated signal, or a combination of one or morethem. The term “data processing apparatus” encompasses all apparatus,devices, and machines for processing data, including by way of example aprogrammable processor, a computer, or multiple processors or computers.The apparatus can include, in addition to hardware, code that creates anexecution environment for the computer program in question, e.g., codethat constitutes processor firmware, a protocol stack, a databasemanagement system, an operating system, or a combination of one or moreof them. A propagated signal is an artificially generated signal, e.g.,a machine-generated electrical, optical, or electromagnetic signal thatis generated to encode information for transmission to suitable receiverapparatus.

A computer program (also known as a program, software, softwareapplication, script, or code) can be written in any form of programminglanguage, including compiled or interpreted languages, and it can bedeployed in any form, including as a stand-alone program or as a module,component, subroutine, or other unit suitable for use in a computingenvironment. A computer program does not necessarily correspond to afile in a file system. A program can be stored in a portion of a filethat holds other programs or data (e.g., one or more scripts stored in amarkup language document), in a single file dedicated to the program inquestion, or in multiple coordinated files (e.g., files that store oneor more modules, sub programs, or portions of code). A computer programcan be deployed to be executed on one computer or on multiple computersthat are located at one site or distributed across multiple sites andinterconnected by a communication network.

The processes and logic flows described in this document can beperformed by one or more programmable processors executing one or morecomputer programs to perform functions by operating on input data andgenerating output. The processes and logic flows can also be performedby, and apparatus can also be implemented as, special purpose logiccircuitry, e.g., an FPGA (field programmable gate array) or an ASIC(application specific integrated circuit).

Processors suitable for the execution of a computer program include, byway of example, both general and special purpose microprocessors, andany one or more processors of any kind of digital computer. Generally, aprocessor will receive instructions and data from a read only memory ora random-access memory or both. The essential elements of a computer area processor for performing instructions and one or more memory devicesfor storing instructions and data. Generally, a computer will alsoinclude, or be operatively coupled to receive data from or transfer datato, or both, one or more mass storage devices for storing data, e.g.,non-volatile solid state storage drives, magnetic, magneto opticaldisks, or optical disks. However, a computer need not have such devices.Computer readable media suitable for storing computer programinstructions and data include all forms of non-volatile memory, mediaand memory devices, including by way of example semiconductor memorydevices, e.g., EPROM, EEPROM, and flash memory devices; magnetic disks,e.g., internal hard disks or removable disks; magneto optical disks; andCD ROM and DVD-ROM disks. The processor and the memory can besupplemented by, or incorporated in, special purpose logic circuitry.

While this patent document contains many specifics, these should not beconstrued as limitations on the scope of any invention or of what may beclaimed, but rather as descriptions of features that may be specific toparticular embodiments of particular inventions. Certain features thatare described in this patent document in the context of separateembodiments can also be implemented in combination in a singleembodiment. Conversely, various features that are described in thecontext of a single embodiment can also be implemented in multipleembodiments separately or in any suitable sub combination. Moreover,although features may be described above as acting in certaincombinations and even initially claimed as such, one or more featuresfrom a claimed combination can in some cases be excised from thecombination, and the claimed combination may be directed to a subcombination or variation of a sub combination.

Similarly, while operations are depicted in the drawings in a particularorder, this should not be understood as requiring that such operationsbe performed in the particular order shown or in sequential order, orthat all illustrated operations be performed, to achieve desirableresults. Moreover, the separation of various system components in theembodiments described in this patent document should not be understoodas requiring such separation in all embodiments.

Only a few implementations and examples are described and otherimplementations, enhancements and variations can be made based on whatis described and illustrated in this patent document.

What is claimed is what is described and illustrated, including:
 1. Asystem for performing geolocation, comprising: a data collectionapparatus in a non-geostationary satellite, the data collectionapparatus includes a processor to implement a method comprising:receiving a number of signals from an earth-based vehicle; determiningarrival times of the number of signals; obtaining position informationof the non-geostationary satellite corresponding to the arrival times ofthe number of signals; and sending, to a signal processing unit, thearrival times and the position information of the non-geostationarysatellite for the number of signals; the signal processing unitconfigured to determine a location of the earth-based vehicle, thesignal processing unit includes a processor to implement a methodcomprising: receiving the arrival times and the position information ofthe non-geostationary satellite for the number of signals; selecting aplurality of candidate locations to determine the location of theearth-based vehicle; and processing the arrival times, the positioninformation, and the plurality of candidate locations to determine thelocation of the earth-based vehicle.
 2. The system of claim 1, whereinthe processing of the arrival times, the position information, and theplurality of candidate locations is performed the signal processing unitby: determining, for each candidate location and based on the arrivaltimes and the position information, an error value that represents aproximity between a candidate location and the location of theearth-based vehicle; and selecting, from the plurality of candidatelocations associated with a plurality of error values, one candidatelocation having a lowest error value, wherein the selected candidatelocation is the determine of the location of the earth-based vehicle. 3.The system of claim 2, wherein the error value is determined for eachcandidate location by the signal processing unit by: determining a firstset of path lengths between the candidate location and each positioninformation of the non-geostationary satellite; determining a second setof path lengths between the location of the earth-based vehicle and eachposition information of the non-geostationary satellite; obtaining afirst error value based on differences between path lengths from thefirst set of path lengths and corresponding path lengths from the secondset of path lengths for each position information of thenon-geostationary satellite; obtaining a second error value based on adifference between earth's radius at a latitude and a longitudeassociated with the candidate location and a magnitude of the candidatelocation's radius, wherein the earth radius and the magnitude of thecandidate location's radius are determined from a same reference point;and determining the error value by combining the first error value andthe second error value.
 4. The system of claim 3, wherein the first setof path lengths are determined by the signal processing unit bycalculating a magnitude of a vector between the candidate location andeach position information of the non-geostationary satellite.
 5. Thesystem of claim 3, wherein the second set of path lengths are determinedby the signal processing unit by multiplying a speed of light by eacharrival time of the number of signals.
 6. The system of claim 3, whereinthe first error value is obtained by the signal processing unit by usinga linear combination of the differences between path lengths from thefirst set of path lengths and corresponding path lengths from the secondset of path lengths for each position information of thenon-geostationary satellite.
 7. The system of claim 3, wherein the errorvalue is determined by the signal processing unit by: multiplying apre-determined value by the second error value raised to a power of twoto obtain a first value; and adding the first value to the first errorvalue raised to a power of two to obtain the error value.
 8. The systemof claim 1, wherein the position information of the non-geostationarysatellite is obtained from a global positioning system (GPS) device orfrom a position determination device located on the non-geostationarysatellite, or wherein the position information of the non-geostationarysatellite is calculated from ephemeris data or ground signal-sourceinformation.
 9. The system of claim 2, wherein the method implemented bythe processor of the signal processing unit further comprises: storingthe selected candidate location for the earth-based vehicle.
 10. Thesystem of claim 1, wherein the number of signals is at least three. 11.The system of claim 2, wherein the selected candidate location providesthe determine of the location of the earth-based vehicle inthree-dimensions.
 12. The system of claim 1, wherein the signalprocessing unit is located in a computing system in a stationaryplatform or in a remote moving platform.
 13. The system of claim 1,wherein the data processing apparatus is configured to perform thedetermining, the obtaining, or the sending in response to receiving aninstruction from a ground-based computing system or from a moving remoteplatform.
 14. A signal processing unit to determine a location of anearth-based vehicle, the signal processing unit includes a processor toimplement a method comprising: receiving arrival times and positioninformation of a non-geostationary satellite associated with a number ofsignals received by the non-geostationary satellite from the earth-basedvehicle; selecting a plurality of candidate locations to determine thelocation of the earth-based vehicle; and processing the arrival times,the position information, and the plurality of candidate locations todetermine the location of the earth-based vehicle.
 15. The signalprocessing unit of claim 14, wherein the processing of the arrivaltimes, the position information, and the plurality of candidatelocations is performed by: determining, for each candidate location andbased on the arrival times and the position information, an error valuethat represents a proximity between a candidate location and thelocation of the earth-based vehicle; and selecting, from the pluralityof candidate locations associated with a plurality of error values, onecandidate location having a lowest error value, wherein the selectedcandidate location is the determine of the location of the earth-basedvehicle.
 16. The signal processing unit of claim 15, wherein the errorvalue is determined for each candidate location by the signal processingunit by: determining a first set of path lengths between the candidatelocation and each position information of the non-geostationarysatellite; determining a second set of path lengths between the locationof the earth-based vehicle and each position information of thenon-geostationary satellite; obtaining a first error value based ondifferences between path lengths from the first set of path lengths andcorresponding path lengths from the second set of path lengths for eachposition information of the non-geostationary satellite; obtaining asecond error value based on a difference between earth's radius at alatitude and a longitude associated with the candidate location and amagnitude of the candidate location's radius, wherein the earth radiusand the magnitude of the candidate location's radius are determined froma same reference point; and determining the error value by combining thefirst error value and the second error value.
 17. The signal processingunit of claim 16, wherein the first set of path lengths are determinedby the signal processing unit by calculating a magnitude of a vectorbetween the candidate location and each position information of thenon-geostationary satellite.
 18. The signal processing unit of claim 16,wherein the second set of path lengths are determined by the signalprocessing unit by multiplying a speed of light by each arrival time ofthe number of signals.
 19. The signal processing unit of claim 16,wherein the first error value is obtained by the signal processing unitby using a linear combination of the differences between path lengthsfrom the first set of path lengths and corresponding path lengths fromthe second set of path lengths for each position information of thenon-geostationary satellite.
 20. The signal processing unit of claim 16,wherein the error value is determined by the signal processing by:multiplying a pre-determined value by the second error value raised to apower of two to obtain a first value; and adding the first value to thefirst error value raised to a power of two to obtain the error value.21. The signal processing unit of claim 15, wherein the methodimplemented by the processor of the signal processing unit furthercomprises: store the selected candidate location for the earth-basedvehicle.
 22. The signal processing unit of claim 14, wherein the numberof signals is at least three.
 23. The signal processing unit of claim15, wherein the selected candidate location provides the determine ofthe location of the earth-based vehicle in three-dimensions.
 24. Thesignal processing unit of claim 14, wherein the signal processing unitis located in a computing system in a stationary platform or in a remotemoving platform.